Question

determine o número de termos da P.G. (1600,800,400,...25)

Answer 1

an = a1 * q^n-1
25 = 1 600 * (1/2)^n-1
1/2^n-1 = 25 / 1 600
1/2^n-1 = 1/64
2^-1(n-1) = 2^-6
-n + 1  = -6
n = 6 + 1
n = 7